Modern electronically controlled appliances have so called capacitive sensors which make it possible to control the appliance by bringing the hand close to or touching a sensor surface. For example, touch-sensitive monitors are known, touching which at a suitable position controls the execution of a computer program displayed on the monitor.
For example, modem electrically or electronically controlled sanitary fittings are additionally based on highly sophisticated, comprehensive electronic circuit arrangements (microprocessors/microcontrollers), which are supplied with energy either by a battery or via a mains voltage converter. Such a control system for sanitary fittings generally has an electrical signal transmitter, in the simplest case a mechanical switch, whose actuation causes the electronic control system to initiate the function of the fitting desired by the user. For example, mention should be made here of actuating a piezoelectric switch in an electronic shower control system, with whose actuation the user can control the water flow, that is to say can start it or possibly also stop it. In addition, in sanitary fittings, infrared reflective light barriers are widespread as signal transmitters for electronic circuit arrangements and, when an object, body, part of a body, etc., is detected in the detection range, a corresponding electrical signal is transmitted by the barriers to a microprocessor control system. Also known are electronically controlled fitting designs which, in addition to a first signal transmitter for the basic function of the fitting, have a further signal transmitter to activate and deactivate further special functions or to change operating parameters. For example, DE-195 08 644 describes the functioning of a control system having a touch switch that is integrated in the fitting and accessible from the outside.
However, because of their low mechanical strength, mechanical signal transmitters for controlling electronic fittings, in particular, are easy to damage from outside the fitting and are therefore susceptible to vandalism. In addition, the mechanical signal transmitters are relatively susceptible to wear, because of contact wear, and therefore have only a limited service life. If they are used in electronic sanitary fittings, it is also necessary to protect the mechanical switches against humidity, which requires complicated insulation and sealing measures, which makes the production of such a fitting complicated and consequently expensive.
On account of the above disadvantages of the mechanically actuated signal transmitters (switches, pushbuttons) for controlling sanitary fittings, in particular, attempts have therefore been made to replace the mechanically actuated signal transmitters by capacitive sensors which, as mentioned above, permit functional control via close approach or touch. Here, for example, reference should be made to U.S. Pat. No. 7,730,165, in which the dispensation of water from a fitting is controlled via a capacitive sensor, which detects the approach of a user to the fitting.
However, such conventional capacitive sensors require extremely complex signal processing electronics, which is associated with correspondingly high costs and a large overall volume. In addition, such capacitive sensors are very susceptible to faults with respect to electrostatic discharges, and electromagnetic irradiation and are extremely sensitive with respect to changes in the dielectric constant in the surrounding media, for example as a result of humidity, wetting, water vapor, and so on, for which reason they can be used only under certain conditions, in particular in the area of sanitary fittings, and also with the provision of correspondingly complex control electronics. In addition, the above conventional capacitive touch sensors need a low-resistance, direct connection between the basic fitting body and the protective conductor potential, which likewise complicates the installation of such fittings and makes it more expensive.
It is therefore an object of the present invention to provide a reliable touch sensor which is constructed as simply as possible and which can also be used in the area of sanitary fittings without problems and cost-effectively.
The object of the present invention is achieved by the features of the independent claims. Advantageous embodiments of the invention are mentioned in the subclaims and/or the following description, which is accompanied by schematic drawings.